The incorporation of antimicrobial agents into various types of materials is beneficial as they may endow the material with the ability to prevent and/or inhibit the growth of microorganisms. Various antimicrobial agents are known. For example, silver is a broad spectrum antimicrobial that is thought to act via irreversible binding of silver ions to nucleophilic groups in the cells of various microbes (i.e., bacteria, viruses, yeast, and fungi). This binding disrupts the reproduction of the cells, resulting in the death of the microbe. Silver (e.g., particular silver and silver coatings) and various silver compounds (e.g., ionic silver compounds) have therefore been incorporated into a variety of wound care products. Silver metal can be used where it can be converted to ionic form. For example, silver in contact with aqueous solutions forms silver oxide, which is slightly soluble in water and can form silver ions.
In addition to silver and silver compounds, inorganic nanoparticles have also elicited significant interest as microbial agents. Nano-structured materials have the potential to achieve specific processes and selectivity, especially in biological and pharmaceutical applications. Certain inorganic nanoparticles have been shown to exhibit novel and improved physical, chemical, and biological properties and functionality due to their nano-scale size. For example, various metal oxide nanoparticles have been shown to have good antimicrobial activity. Certain inorganic particles that have been reported to exhibit antimicrobial properties include nano-silver, various oxides and sulfides of nanomaterials (including titanium dioxide, selenium sulfide, cadmium oxide, and zinc oxide). The antimicrobial mode of action of such nanoparticles may be the targeting of the cellular fabric by hydroxyl radicals, thus increasing permeability, disrupting metabolism, waste excretion, and fabric stability. In some cases, metal oxide nanoparticles may be preferable to nano-silver because of cost considerations. Further, cadmium oxide and titanium dioxide are both non-toxic and chemically stable under exposure to both high temperatures and capable of photo catalytic oxidation.
Poly(tetrafluoroethylene), PTFE, is a thermoplastic that offers exceptional resistance to high temperatures and corrosive environments. Because it is inert and nontoxic, PTFE is often used in medical implants. Although it is useful for numerous applications, PTFE is difficult to process by conventional molten polymer techniques. One method by which PTFE can be processed is by extruding the material as a paste and then drawing it into various forms to produce fibers, ribbons, fabrics, or tubes. PTFE made in this fashion is referred to as “expanded PTFE” or “ePTFE.” One further method for processing of PTFE is to combine PTFE dispersions with fiber forming polymers. The mixture can then be electrospun to produce nonwoven fabrics, coverings, bats, or composites based on nanofibers. These forms of PTFE are commonly sintered, at least in part, at high temperatures to develop desirable mechanical properties. For both ePTFE and electrospun PTFE, a porous structure is created with high surface area.
Electrostatic spinning is a known process, as illustrated, for example, in U.S. Pat. Nos. 2,158,416 to Formhals; 4,043,331 to Martin et al.; 4,044,404 to Martin et al.; 4,143,196 to Simm et al.; 4,287,139 to Guignard; 4,323,525 to Bornat; 4,432,916 to Logan; 4,689,186 to Bornat; and 6,641,773 to Kleinmeyer et al., and U.S. Patent App. Publ. No. 2010/0193999 to Anneaux et al., each of which is incorporated herein by reference in their entirety.
Due to the wide application of PTFE in medical and other applications, it would be beneficial to incorporate antimicrobial agents within PTFE to endow the material with antimicrobial properties. Both organic and inorganic antimicrobial agents have been previously incorporated into PTFE articles by soaking or coating the exterior of the article with ionic silver or silver metal. However, such coatings are difficult to apply and have a relatively short product life. Thus, there is a need for a means by which antimicrobial agents can be incorporated effectively and easily into PTFE.